This invention relates to a process for recovering 18-methyl eicosanoic acid (18-MEA) and/or alpha hydroxy acids from woolwax acids or derivatives thereof. These materials can be employed as active ingredients in personal care products.
By xe2x80x9calpha hydroxy acidsxe2x80x9d, we mean acids of the formula: 
where R can be CH3 or H and n is in the range 10 to 22.
The formula of 18-MEA is: 
Woolwax is the preferred name for the fat or grease found in the wool of sheep, Ovis aries. In its virgin unrefined state it is one of the best preventatives for rust, but generally woolwax is refined by chemical processing into commercially useful materials in one of two ways. Firstly, it is purified by a refining procedure to give Lanolin. Lanolin is the refined version of woolwax and is used primarily in a hydrated version as an emollient to soothe, smooth and calm dry or damaged skin. Secondly, the woolwax can be saponified to provide separate alcohol and acid fractions. The alcohol fraction is a complex mixture of sterols and fatty alcohols. This fraction has numerous uses, primarily to give emollient and emulsification properties to products in the personal care industry. By contrast, however, the woolwax acid fraction, although utilised to some extent in the personal care industry, has not found the same number of end user markets. This may in part be due to the highly complex nature of the fatty acids within the woolwax acid fraction which would by convention be considered as an impure source of fatty acids when compared to the use of oil seed triglycerides or tallow. Woolwax acids have a complex lipid profile consisting of iso, ante-iso and normal fatty acids and iso and nonnal alpha hydroxy fatty acids having carbon backbone skeletons ranging in carbon chain length from eight to thirty carbon atoms. More specifically the iso and normal alpha hydroxy fatty acid carbon backbone skeletons range in carbon chain length from fourteen to twenty six carbon atoms. Table 1.0 (hereinafter) shows the typical fatty acid groups within the woolwax acid lipid profile and also indicates the typical total levels of these groups within the said profile. The most abundant fatty acid within the woolwax acid composition is alpha hydroxy palmitic acid which ranges from 10% w/w to 16% w/w and, more particularly, 11% w/w to 14% w/w.
As the understanding of cosmetic ingredients and their potential modes of action have advanced, a market requirement has developed for specifically purified fractions of the woolwax acids. For example, the alpha hydroxy acid (AHA) components are believed to reduce the symptoms of skin ageing that result from sun exposure and other environmental factors. The effects of the AHA""s within an emollient based cream are met with reductions in the following symptoms, mottled hyperpigmentation, fine and course wrinkling, laxity, sallowness, telangiectasia and tactile roughness. The AHA product is believed to exhibit these improvement qualities only when correctly formulated. In the case of reducing skin roughness, for example, the mode of action is by limiting the degree of transepidermal water loss.
Contained within the ante-iso fatty acid homologues of the woolwax acid fraction is the important lipid 18-MEA. This is a major structural lipid found as the major fatty acid species within the hair lipid matrix of mammalian hair (D. J. Fleet, R. E. H. Wettenhall, D. E. Rivett and A. K. Allen; A comparative study of covalently-bound fatty acids in keratinized tissues, Comp. Biochem. Physiol, Vol 102B, No.2, 363-366, (1992). This ante-iso fatty acid has been demonstrated as the active ingredient when formulated within hair care products. 18-MEA is also found as part of the wax ester matrix which makes up Woolwax. The long chain ante-iso fatty acid is typically found at levels of 1% w/w to 4% w/w of the woolwax acids, though more usually at levels of 2% w/w to 3.5 w/w.
Because of the commercial interest in 18-MEA and the AHA""s, efforts have been made to obtain purified versions of these materials. For example, the isolation of AHA""s from woolwax and woolwax acids has been attempted using various approaches eg. transit metal chelation (A. H. Milburn and E. V. Truter, Extraction of 2-hydroxy acids from Wool Wax Acids, J. Appl. Chem; 12, 156-160 (1962) and solvent fractionation (Downing, Solvent Fractionation of Wool Wax Acids, Aust. J Appl. Sci., 14 (No. 1) 50-56, (1962), and Beiersdorf A G, EP-A-555776).
A complicating factor in the separation of AHA""s from woolwax and woolwax acids is the thermal instability of the AHA moiety due to the presence of the hydroxyl functionality in the alpha position which not increase the acidity of the carboxylic acid group but also gives a centre for further side reactions. This thermal lability results in the formation of lactones/estolides and polymers. The net result of these reactions means that the woolwax acid has a significant reduction in the total amount of AHA that can be recovered. This degradation is well documented (see for example W. R. Noble, A. Eisner and J. T. Scanlan, isolation of a Hydroxy Acid Concentrate from Wool Wax Acids, JAOCS, 37, 14-16, (1960)).
As far as 18-MEA is concerned, the concentration of this component in woolwax acid is fairly low, typically in the range of 1 to 4% w/w and more specifically 2.5 to 3.5% w/w. These variations are accounted for according to the geographical location of the raw material and the breed of sheep from which the woolwax was scoured. It would also appear that little work has been carried out for the isolation of this material from woolwax. Work has been done to isolate the integral 18-MEA from the hair lipid matrix of mammalian hair but, this is not a commercial route since it does not permit the recovery of large enough quantities of the acid for the personal care market. Attempts have been made to synthesise 18-MEA but, in general, these involve complex multistep processes which inevitably result in low yielding routes to the desired product. The synthetic material also faces the problem of being accepted within the personal care sector as it has not been derived from a natural source which automatically places it at a disadvantage.
It is therefore, highly desirable to achieve a cost effective and robust process to isolate both an AHA enriched and an 18-MEA enriched lipid blend directly from woolwax acids.
According to the present invention, there is provided a process for recovering 18-methyl eicosanoic acid (18-MEA) and/or alphahydroxy acids from woolwax acids or derivatives thereof, which comprises heating the woolwax acids or derivatives thereof to 100xc2x0 to 230xc2x0 C. to form estolides and polymeric species; distilling to obtain a distillate and a residue; and recovering 18-MEA from the distillate and/or recovering alpha hydroxy acids from the residue.
The process of the invention surprisingly relies for its selectivity on the ability of the AHA""s to form the estolide and polymeric species. This has hitherto been seen as an undesirable feature in the isolation of AHA""s from woolwax.
The preferred feedstock of the invention is the woolwax acids as obtained from saponification of woolwax, but certain derivatives of woolwax acids can also be used as the feedstock for this invention, provided that the derivatives form estolides and polymers upon heat treatment. Suitable derivatives would be esters involving the acid functionality of the woolwax and/or esters of the hydroxyl functionality of the AHA""s. Examples of suitable derivatives would include methyl, ethyl and propyl esters of the woolwax fatty acids, and formates and acetates of the AHA""s within the woolwax acid mixtures. Preferably, woolwax acids are used as this involves fewer processing steps and in this way gives the 18-MEA concentrate in the more desirable free acid form. The form of the AHA has no consequence as the saponification step hydrolyses directly to the free fatty acid.
In the process of the invention, the woolwax acid (or derivatives) feedstock is heated to 100xc2x0 C. to 230xc2x0 C., preferably 150xc2x0 C. to 200xc2x0 C., most preferably 160xc2x0 C. to 180xc2x0 C. The heating is generally maintained for about 1 to 48 hours, preferably 3 to 16 hours, and most preferably 5 to 10 hours. A vacuum can be used to displace the equilibrium towards estolide/polymer formation. A catalyst may be used at this stage but we have found that the reaction will proceed well uncatalysed. If a catalyst is used, however, then conventional esterification catalysts such as sodium hydroxide, sodium methoxide, sodium ethoxide, potassium hydroxide, potassium tert-butoxide, mineral acids like phosphorus acids, for example phosphoric acid or hypophosphorus acid, sulphuric acid, hydrochloric acid, and organic acids like methane sulphonic acid and p-toluene sulphoric acid, are suitable. These catalysts are merely examples as will be appreciated by those skilled in the art, and any suitable material that speeds up the desired reaction may be employed for the purposes of catalysing the reaction, providing the desired final polymeric material is prepared.
Following the interesterification reaction, the product is distilled under vacuum, preferably less than 1xc3x9710xe2x88x921 mbar and most preferably less than 1xc3x9710xe2x88x922 mbar, at a temperature of between 150xc2x0 and 250xc2x0 C. to yield a distillate (D1) depleted in AHA""s and a residue (R1) comprising essentially interesterified AHA""s. The distillation can be a separate stage or a direct stage. The separate procedure is described in full below and an example of a direct procedure is given in the Examples. The interesterification and total distillation can be achieved in a vessel capable of handling vacuums of the level described.
Following the distillation, the AHA""s may be recovered from the residue (R1). Thus, for example, the residue may be saponified to yield the fatty acid soaps of the AHA""s. This saponification can, for example, be carried out using an alcoholic solution of an appropriate base, for example sodium or potassium hydroxide, in water but it will be appreciated by those skilled in the art that other conditions can equally be used. The soaps may then be purified such as by solvent extraction. We have used n-hexane to extract the unsaponifiable components from the aqueous alcoholic solution of the soaps but it will be appreciated that any solvent which is immiscible with the aqueous alcoholic phase and has sufficient solubility for the unsaponifiable by-products, can be used. Examples include, for example, petroleum ether 40/60 bp., petroleum ether 60/80 bp and diethylether. The purified soaps can then be acidified to regenerate the free fatty acid. The types of acid that can be used for the purposes of hydrolysing the soaps are not limited to the more common mineral acids, for example hydrochloric acid and sulphuric acids, but as will be appreciated by those skilled in the art, any strong acid can be used either as a solution or as a bound acid, for example an ion exchange resin.
The free AHA concentrate thus obtained may be further purified by distillation under vacuum, preferably less than 1xc3x9710xe2x88x921 mbar and most preferably less than 1xc3x9710xe2x88x922 mbar, at a temperature of between 100xc2x0 C. and 230xc2x0 C., preferably between 110xc2x0 and 200xc2x0 C. and most preferably between 120xc2x0 C. and 180xc2x0 C., to yield a distillate (D2) elevated in AHA""s and a residue (R2) essentially comprising high molecular weight fatty acids and some interesterified AHA""s. The concentration of AHA""s in the purified product (D2) will depend on the concentration of AHA""s within the original raw material woolwax acids which is itself a natural product and will of course be variable. However, typically we would expect the ratio of AHA% in the purified product to AHA% in the raw material, to be in the range of about 1.1 to 3.0, more preferably 1.3 to 2.5, and most preferably 1.7 to 2.2.
The 18-MEA lipid fraction can be derived by processing the distillate (D1) in a number of different ways. We prefer to use either distillation, urea inclusion complexation or chromatographic refining, or a combination of the three processes to obtain the desired 18-MEA level within the final concentrate. Our preferred route is that of distillation followed by chromatographic-refining as this has less environmental impact with respect to the disposal of the waste inclusion complex, namely the urea and waste fatty acid. If an inclusion complex agent is to be used, it must be appreciated by those skilled in the art that any conventional inclusion forming complex agent can be used under appropriate conditions.
The distillate (D1) obtained as described above may be further purified b distillation under vacuum preferably less than 1xc3x9710xe2x88x921 mbar and most preferably less than 1xc3x9710xe2x88x922 mbar at a temperature of between 100xc2x0 C. and 230xc2x0 C., preferably between 110xc2x0 C. and 200xc2x0 C. and most preferably between 120xc2x0 C. and 180xc2x0 C., to yield a distillate (D3) elevated in 18-MEA and a residue (R3) comprised essentially of higher molecular weight fatty acids and low levels of interesterified AHA""s. Clearly, the concentration of 18-MEA in the purified product (D3) will depend on the concentration of 18-MEA within the original raw material woolwax acids which is itself a natural product and will of course be variable. However, typically we would expect the ratio of 18-MEA% in the purified product to 18-MEA % in the raw material, to be in the range of about 1.1 to 1.5.
The distillate (D3) thus obtained may be further purified by distillation under vacuum, preferably less than 1xc3x9710xe2x88x921 mbar and most preferably less than 1xc3x9710xe2x88x922 mbar, at a temperature of between 80xc2x0 C. and 230xc2x0 C., preferably between 95xc2x0 C. and 190xc2x0 C. and most preferably between 105xc2x0 C. and 160xc2x0 C., to yield a distillate (D4) depleted in 18-MEA and a residue (R4) comprising an elevated level of 18-MEA. Clearly the amount of 18-MEA in the purified residue (R4) will depend on the concentration of 18-MEA within the previous distillate (D3) which will also be affected by the concentration of 18-MEA within raw material woolwax acids which is itself a natural product and will of course be variable. However, typically we would expect the ratio of 18-MEA % in the purified residue (R4) to 18-MEA % in the raw material, to be in the range of about 1.0 to 10.0, more specifically in the range 2.0 to 5.0. It will also be appreciated that the distillation conditions can be altered in any combination and are not limiting. For example conditions can be used where the residue (R3) contains the elevated levels of 18-MEA and then the distillate (D4) also has elevated levels of 18-MEA.
Any 18-MEA concentrate can be chromatographically refined to give a desired product specification. Usually the 18-MEA fatty acid concentrate is solubilised in an appropriate solvent. One suitable solvent is n-hexane but it will be appreciated that any solvent which is miscible with the fatty acid with sufficient solubility power will be suitable, for example petroleum ether 40/60 bp., petroleum ether 60/80 bp or diethylether, can be used. In our process, we prefer to dissolve about 1 part fatty acid in about 1 part solvent, though the degree of solute concentration within solvent is not critical. The process can be performed at any temperature provided a complete solution is maintained. If the solution is to be heated, it is preferably performed safely at the appropriate temperature below the boiling point of the solvent. The fatty acid solution is then passed through an appropriate inert absorbent earth to remove the odour bodies, colour bodies and polar species from the solution. The amount of earth that is used depends on the degree of colour improvement or, odour removal that is required. Typically the ratio of fatty acid used to earth used is in the range of about 0.5 to 4.0, preferably 0.9 to 2.0 and most preferably 1.0 to 1.5. This process can also be used to further concentrate the 18-MEA which depends to some extent on the ratio of fatty acid used to earth used, which dictates how much material is absorbed onto the earth. For example, if 8% of polar fatty acids are totally removed by the earth from the original fatty acid mixture, the level of 18-MEA will be further elevated by 8% W/W.
The distillates (D1and D3) and residue (R4) may be further purified by removing the normal saturated fatty acids by formation of inclusion complexation from the fatty acid mixtures. We prefer to use urea as the inclusion complex forming agent and industrial methylated spirits as the solvent, but it will be appreciated by those skilled in the art that these conditions/reagents are not critical. Typically the ratio of urea to industrial methylated spirits is in the range of 1 to 10, preferably 2 to 8 and most preferably 3 to 5. The ratio of distillates (D1or D3) or residue (R4) to urea is also not critical and typically the range is about 0.25 to 10, preferably 0.75 to 4 and most preferably 1 to 3.
In a further aspect of the invention there is provided a cosmetic product containing 18-MEA or an AHA produced according to the process of the present invention. The cosmetic product may be included in compositions for hair treatment, such as shampoos, conditioners, permanent waves, or for skin treatment, for example creams, lotions, serums and make-up.
In order that the invention may be more fully understood, the following Examples are given by way of illustration only.